SmogRank / Episodes / Thailand
North-western Thailand and Laos, April 2023
For 2 days, from 7 to 8 April 2023, 16 cities in Thailand and Laos had PM2.5 at least twice their usual for the time of year. The worst reading was Mae Sai, Chiang Rai, Thailand: 345.0 µg/m³ on 7 April, about 4.5× its usual 76.4.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 16 in 2 countries
Days 2 7 to 8 April 2023
Worst day 7 April 14 cities counted
Furthest above usual 4.5× Mae Sai
Day by day
Play 7 April 14 cities at twice their usual or more
Uttaradit Phetchabun Phichit Khon Kaen Tak Kamphaeng Phet Kalasin Sakon Nakhon Mae Sot Mukdahan Udon Thani Phrae Vientiane Lamphun Sukhothai Pakxan Lampang Tha Bo Nong Bua Lamphu Nan Phayao Chiang Rai Chiang Mai Ban Houakhoua Loei Mae Sai 4 Apr 5 6 7 8 9 10 11 Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.
How it spread
Mae Sai Mae Sai, 4 April: 198.0 µg/m³, 2.6× usual Mae Sai, 5 April: 229.0 µg/m³, 3.0× usual Mae Sai, 6 April: no reading Mae Sai, 7 April: 345.0 µg/m³, 4.5× usual Mae Sai, 8 April: 326.0 µg/m³, 4.3× usual Mae Sai, 9 April: 249.0 µg/m³, 3.3× usual Mae Sai, 10 April: 163.0 µg/m³, 2.1× usual Mae Sai, 11 April: 184.0 µg/m³, 2.4× usual Tha Bo Tha Bo, 4 April: 130.0 µg/m³, 2.5× usual Tha Bo, 5 April: 111.0 µg/m³, 2.1× usual Tha Bo, 6 April: 182.0 µg/m³, 3.5× usual Tha Bo, 7 April: 146.0 µg/m³, 2.8× usual Tha Bo, 8 April: 50.3 µg/m³, 1.0× usual Tha Bo, 9 April: 37.0 µg/m³, 0.7× usual Tha Bo, 10 April: 66.4 µg/m³, 1.3× usual Tha Bo, 11 April: 90.7 µg/m³, 1.8× usual Vientiane Vientiane, 4 April: 130.0 µg/m³, 2.4× usual Vientiane, 5 April: 111.0 µg/m³, 2.0× usual Vientiane, 6 April: 182.0 µg/m³, 3.3× usual Vientiane, 7 April: 146.0 µg/m³, 2.6× usual Vientiane, 8 April: 50.3 µg/m³, 0.9× usual Vientiane, 9 April: 37.0 µg/m³, 0.7× usual Vientiane, 10 April: 66.4 µg/m³, 1.2× usual Vientiane, 11 April: 90.7 µg/m³, 1.6× usual Ban Houakhoua Ban Houakhoua, 4 April: 166.0 µg/m³, 1.9× usual Ban Houakhoua, 5 April: 182.0 µg/m³, 2.1× usual Ban Houakhoua, 6 April: no reading Ban Houakhoua, 7 April: no reading Ban Houakhoua, 8 April: 317.0 µg/m³, 3.7× usual Ban Houakhoua, 9 April: no reading Ban Houakhoua, 10 April: no reading Ban Houakhoua, 11 April: 142.0 µg/m³, 1.6× usual Chiang Mai Chiang Mai, 4 April: 93.8 µg/m³, 1.5× usual Chiang Mai, 5 April: 128.5 µg/m³, 2.0× usual Chiang Mai, 6 April: no reading Chiang Mai, 7 April: 223.0 µg/m³, 3.5× usual Chiang Mai, 8 April: 188.0 µg/m³, 3.0× usual Chiang Mai, 9 April: 134.0 µg/m³, 2.1× usual Chiang Mai, 10 April: 115.0 µg/m³, 1.8× usual Chiang Mai, 11 April: 120.0 µg/m³, 1.9× usual Phrae Phrae, 4 April: 77.0 µg/m³, 1.4× usual Phrae, 5 April: 115.0 µg/m³, 2.0× usual Phrae, 6 April: no reading Phrae, 7 April: 135.0 µg/m³, 2.4× usual Phrae, 8 April: 99.9 µg/m³, 1.8× usual Phrae, 9 April: no reading Phrae, 10 April: no reading Phrae, 11 April: 67.3 µg/m³, 1.2× usual Loei Loei, 4 April: 85.1 µg/m³, 1.7× usual Loei, 5 April: 104.0 µg/m³, 2.1× usual Loei, 6 April: no reading Loei, 7 April: 215.0 µg/m³, 4.2× usual Loei, 8 April: 212.0 µg/m³, 4.2× usual Loei, 9 April: 80.3 µg/m³, 1.6× usual Loei, 10 April: 68.7 µg/m³, 1.4× usual Loei, 11 April: 72.7 µg/m³, 1.4× usual Pakxan Pakxan, 4 April: 46.7 µg/m³, 1.0× usual Pakxan, 5 April: 101.0 µg/m³, 2.1× usual Pakxan, 6 April: no reading Pakxan, 7 April: 132.0 µg/m³, 2.7× usual Pakxan, 8 April: 56.2 µg/m³, 1.2× usual Pakxan, 9 April: 33.4 µg/m³, 0.7× usual Pakxan, 10 April: 42.6 µg/m³, 0.9× usual Pakxan, 11 April: 58.2 µg/m³, 1.2× usual Phayao Phayao, 4 April: 112.0 µg/m³, 1.5× usual Phayao, 5 April: 145.0 µg/m³, 2.0× usual Phayao, 6 April: no reading Phayao, 7 April: 236.0 µg/m³, 3.2× usual Phayao, 8 April: 186.0 µg/m³, 2.6× usual Phayao, 9 April: no reading Phayao, 10 April: no reading Phayao, 11 April: 93.3 µg/m³, 1.3× usual Chiang Rai Chiang Rai, 4 April: 117.0 µg/m³, 1.8× usual Chiang Rai, 5 April: 118.0 µg/m³, 1.8× usual Chiang Rai, 6 April: no reading Chiang Rai, 7 April: 228.0 µg/m³, 3.4× usual Chiang Rai, 8 April: 227.0 µg/m³, 3.4× usual Chiang Rai, 9 April: 169.0 µg/m³, 2.6× usual Chiang Rai, 10 April: 126.0 µg/m³, 1.9× usual Chiang Rai, 11 April: 140.0 µg/m³, 2.1× usual Nan Nan, 4 April: 99.6 µg/m³, 1.3× usual Nan, 5 April: 139.0 µg/m³, 1.8× usual Nan, 6 April: no reading Nan, 7 April: 228.0 µg/m³, 3.0× usual Nan, 8 April: 161.0 µg/m³, 2.1× usual Nan, 9 April: no reading Nan, 10 April: no reading Nan, 11 April: 90.0 µg/m³, 1.2× usual Lampang Lampang, 4 April: 80.9 µg/m³, 1.2× usual Lampang, 5 April: 120.0 µg/m³, 1.8× usual Lampang, 6 April: no reading Lampang, 7 April: 182.0 µg/m³, 2.7× usual Lampang, 8 April: 147.0 µg/m³, 2.2× usual Lampang, 9 April: no reading Lampang, 10 April: no reading Lampang, 11 April: 86.7 µg/m³, 1.3× usual Lamphun Lamphun, 4 April: 69.4 µg/m³, 1.0× usual Lamphun, 5 April: 96.6 µg/m³, 1.4× usual Lamphun, 6 April: no reading Lamphun, 7 April: 176.0 µg/m³, 2.6× usual Lamphun, 8 April: 135.0 µg/m³, 2.0× usual Lamphun, 9 April: no reading Lamphun, 10 April: no reading Lamphun, 11 April: 82.0 µg/m³, 1.2× usual Sukhothai Sukhothai, 4 April: 41.9 µg/m³, 0.9× usual Sukhothai, 5 April: 50.1 µg/m³, 1.1× usual Sukhothai, 6 April: no reading Sukhothai, 7 April: 124.0 µg/m³, 2.6× usual Sukhothai, 8 April: 89.8 µg/m³, 1.9× usual Sukhothai, 9 April: 51.1 µg/m³, 1.1× usual Sukhothai, 10 April: 73.0 µg/m³, 1.5× usual Sukhothai, 11 April: 69.0 µg/m³, 1.5× usual Nong Bua Lamphu Nong Bua Lamphu, 4 April: 50.9 µg/m³, 1.3× usual Nong Bua Lamphu, 5 April: 70.1 µg/m³, 1.8× usual Nong Bua Lamphu, 6 April: no reading Nong Bua Lamphu, 7 April: 113.0 µg/m³, 2.9× usual Nong Bua Lamphu, 8 April: 87.0 µg/m³, 2.2× usual Nong Bua Lamphu, 9 April: no reading Nong Bua Lamphu, 10 April: 50.3 µg/m³, 1.3× usual Nong Bua Lamphu, 11 April: 53.1 µg/m³, 1.3× usual Udon Thani Udon Thani, 4 April: 50.9 µg/m³, 1.3× usual Udon Thani, 5 April: no reading Udon Thani, 6 April: no reading Udon Thani, 7 April: no reading Udon Thani, 8 April: 82.4 µg/m³, 2.1× usual Udon Thani, 9 April: 35.2 µg/m³, 0.9× usual Udon Thani, 10 April: 40.3 µg/m³, 1.0× usual Udon Thani, 11 April: 51.3 µg/m³, 1.3× usual 4 Apr 5 6 7 8 9 10 11 Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Mae Sai Chiang Rai, Thailand 2 7 April 76.4 4.5× Loei Loei, Thailand 2 7 April 50.7 4.2× Ban Houakhoua Bokeo, Laos 1 8 April 86.8 3.7× Chiang Mai Chiang Mai, Thailand 2 7 April 63.2 3.5× Tha Bo Nong Khai, Thailand 1 6 April 51.7 3.5× Chiang Rai Chiang Rai, Thailand 2 7 April 66.1 3.4× Vientiane Vientiane Prefecture, Laos 1 6 April 55.1 3.3× Phayao Phayao, Thailand 2 7 April 72.8 3.2× Nan Nan, Thailand 2 7 April 75.7 3.0× Nong Bua Lamphu Nong Bua Lamphu, Thailand 2 7 April 39.4 2.9× Pakxan Bolikhamsai, Laos 1 7 April 48.2 2.7× Lampang Lampang, Thailand 2 7 April 67.6 2.7× Sukhothai Sukhothai, Thailand 1 7 April 47.1 2.6× Lamphun Lamphun, Thailand 2 7 April 67.8 2.6× Phrae Phrae, Thailand 1 7 April 56.1 2.4× Udon Thani Udon Thani, Thailand 1 8 April 39.3 2.1×
Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.
Against other episodes in Thailand and Laos
Number 13 of 24 episodes in Thailand and Laos since our records began, by cities reached.
Central Thailand, March 2025 53 Western Thailand, February 2024 51 Central Thailand, January 2025 50 North-western Thailand, April and May 2024 45 North-western Thailand, May 2023 41 Western Thailand, April 2023 35 Western Thailand and Laos, January and February 2023 34 North-western Thailand, May 2023 30 North-eastern Thailand, October 2024 24 Northern Thailand, November and December 2025 22 Western Thailand, February 2025 17 North-western Thailand, May 2023 17 North-western Thailand and Laos, April 2023 16 Bars: cities reached; colour: the level of the episode's highest daily reading. All 24 .
Use this page SmogRank, North-western Thailand and Laos, April 2023: 16 cities with PM2.5 at twice their usual or more, 7 to 8 April 2023, smogrank.com/episodes/2023-04-north-western-thailand-and-laos (accessed 3 October 2026).
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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms .
An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes . Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.
